Yup, they are 3rd. Try a little series inductance or parallel
capacitance. A few pf of cap. may do the trick. Basically these were
usually cut for 25 pf load versus the usual 32 or so of fundamental
rocks. BTW the fundamental will not be at exactly one third of the
overtone freq. (I don't remember why) You may very well have a bad
xtal too, it happens quite often. Good Luck, Mike